A modern up to the minute new Airliner crashed killing all onboard with two qualified drivers at the wheel/s. That opens a whole Pandora's box as to why?
Investigators will look at them ALL!
Crew, broken down individually covering a huge raft of sub conditions such as fatigue, health/medical inc mental. Experience, training etc etc.
Airframe serviceability
Engines.
Fuel, type & condition.
Maintenance especially recent Maint including washing of the airframe.
Sabotage/interference. Remember the Ethiopian Flt 961 B767 hijack some years ago?. Hijacked from exactly the same route as this crash!
Weather.
It could be anyone of these or multiple, Boeing am sure are somewhat nervous as they should be!
Hope they get to the bottom of the cause, nobody wins here, we just have a lot of devastated people! & mass confusion:-(